Acceleration of breech bolts in machine guns



Jan. 18, 1949. c. E. BALLEISEN ACCELERATION OF BREECH BOLTS IN MACHINE GUNS 3 Sheets-Sheet l Filed May 2, 194e Sme/ww Lvl ko. @www CHARLES: E EIALLEISEN @Wl/Mww aan Jan. 18, 1949. c. E. BALLEISEN ACCELERATION OF BREECH BOLTS IN MACHINE GUNS 3 Sheets-Sheet 2 Filed May 2, 1946 SWW/Wto@ CHARLES. E EIALLE IEE N fama Jan. 18, 1949.

C. E. BALLEISEN ACCELERATION 0F BREECH BQLTS IN MACHINE GUNS 3 .Sheets-Sheet 3 Filed May 2, 1946 :D A .0% Nm G n .vxv kb EHARLEEJ E EJALLEIEEN @www Patented Jan. 18, 1949 NITED STATES :PATENT GFFICE ACCELERATION OF BREECH BOLTS IN MACHINE GUNS Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The invention relates to improvement in high speed machine guns, particularly such as the Browning gun, and has for an Object to enable increase of the rate of nre in a degree far beyond that attainable by adjustment of the parts in prior such gun actions. The invention in its present embodiment is applied specically to an improvement of the Browning machine gun, caliber .50, M2, as heretofore used in the United States Army, this weapon being substantially illustrated in the patents to Browning Numbers 1,293,022 and 1,628,226.- It is an object of the invention to attain increase in the rate of fire by means beyond the mere reduction in weight of parts or increase of recoil forces from the propellent explosives used in the ammunition for the guns. It is also a highly important aim of the invention to enable the high increase in rate of re without changing the size and contours or operative connections and mountings of the principal parts of the gun named, but principally by modication of form of the accelerator heretofore used, without requiring any change in the mounting of the accelerator, but permitting its installation upon the same mounts, and in substantially the same weight, without change of the form or proportions of the barrel extension heretofore used, or of the bolts as heretofore used.

, As is known, in the above mentioned weapon, the bolt and barrel are not locked against recoil, but the necessary reaction to attain the required projectile velocity is effected by providing adequate mass in the bolt and recoiling barrel parts so that the inertia of these parts in counterrecoil will oppose the pressures in the chamber for a sufficient time to develop the desired external ballistic values of the ammunition. In increasing the speed of recoil to attain a material increase in rate of re, an equivalent momentum will give rise to the required higher velocities if there is less weight in the recoiling parts. Even at the slower speeds of the prior gun, the recoiling parts were subjected to severe shocks in vthe stoppages and accelerations required,v and with the increased rates of movement of these parts involved in the new gun, these shocks would have been so increased as to involve early destruction, without the inclusion of some means by-whichsuch tendencies are overcome. It istherefore a highly important purpose of the present invention topreamended April 30, 1928; 370 0. G. 757) sent a construction'involving slight modication in minor parts, by which the bolt, barrel, and accelerator devices are saved from damaging shocks and the gun enabled to operate safely and with long life at speeds exceeding a increase as compared to priormaximum rates.

It is an important aim of the invention to enable the improvements in safe operation atl high rates of fire of a gun action utilizing principal parts of the prior gun in identical size and form, but of slightly less weight, and with only a modification of a few small easily produced parts, so that quantity productionwmay be continued with a minimum delay and so avoid millions of dollars of expense in redesigning, retooling of manufacturing plants, and other attendant expenses which would otherwise -bev involved.

My invention is of importance in connection with failures of the gun as heretofore constructed when operated at high firing rates, inasmuch as the most common diiiiculty listed in the firing records wasv a failure to feed, this comprising more than thirty-five percent of all stoppages encountered. The principal cause of this stoppage was the lack of power in the feed mechanism to overcome inertia of the belt and rounds quickly enough at the greater speeds involved in increased ring rates. Therefore, it is an object of the invention to provide an improvement in the construction of the accelerators whereby, through greater acceleration, the necessary additional force may be developed in recoil and stored for effective actuation of the ammunition feed on counterrecoil. It is possible to use a more powerful driving spring to store this additional energy, although, due to the lightening of the bolt, counterrecoil -with a higheffectiveness may still be attained with the same driving spring heretofore used, and a more powerful bolt buffer used.

Incident to theincreased rates of re attained with my invention, improvement in the formation of parts to avoid damage by the greater stresses involved in stoppages and contacts of parts may be required, andthese may be incorporated as discretion or experience may indicate, some ofwhich are shown in the accompanying drawings. The improvement of vthefunction of the accelerators resulting from this -invention involves more than amere variation of their radius or the mere increase of velocity in the barrel extension and bolt in operating them.` The kinematic functions of the prior accelerator have been highly unsatisfactoryespecially when increased rate of fire was attempted. The prior theory appears to have been that a simple leverage acentire accelerating force, after which the bolt leaped away from the accelerator. Guns functioning in this way were used for at least thirty years. In consequence, it is an essential Vaim of the invention to effect application of accelerating 'force to the bolt'by the accelerator without material shock at its initiation, andto continue the acceleration over increased period of time relative to the total recoil period of the bolt.

In the functioning of the prior accelerators, breakage of the accelerator tips was more or lessk rfrequent due to the high impact of its initial contact with the bolt. This tendency is overcome here by reason of the improved timing oi the bearing of the yaccelerator on the barrel extension and bolt, and also by any improved proportioning of the accelerator in relation to the initial recoil positions oi the barrel extension and bolt. One feature of this improvement is the attainment of the beginning of acceleration while rearward motions of the barrel extension, accelerator tips, and bolt are coincident or practically so. At the same time it is made possible to include in the accelerator a greatly strengthened body part between the points of initial accelerating contacts of the barrel extension and bolt with the accelerator, so that withthe decrease of impact stress at Vthis `time and the increased strength of the accelerator, liability of fracture is practically eliminated, notwithstanding the high ring rates attained (which have exceeded by 50% prior high firing rates with the unmodified M2 gun). In addition to these improvements, a fault in the prior` accelerator whereby it vibrated or chattered severely during recoil of the bolt, after the barrel had come to rest, andA while the bolt was passingover the accelerator, has been cured. This resulted in severe wear of the under-surface of the bolt in spots, and was evi i dent in all guns after a moderate period of use. The proportioning of the new accelerator has a novelA coordination with the clearance between the locked accelerator and the under-surface of the bolt during recoil whereby such chattering is 55 prevented.

In the prior gun and also in the gun asV improved by me, the projectile and also most of the gases, leave the muzzle 'of the gun sometime before the accelerator i-lrst begins to displace the bolt with respect to the barrel extension, greater time Velapsing in the earlier gun. Consequently,

only the momentum and mass of the moving parts is available for the force used to extract the spent cartridge case, accelerate the bolt, and store in the driving spring and buffer spring the energy to feed and to position the new round, and fire it, In the prior accelerator, at initial acceleration of the bolt the barrel extension applied the force from the recoiling barrel unit to the bolt and the accelerator pin in a ratio of about 3A to the bolt and 1A; to the accelerator pin.v In my device, practically the entire initial accelerating force of the recoi-ling barrel extension `is applied to the bolt; i f

In the earlier weapon the pressure in the oil buffer had been built up substantially when acceleration of the bolt relative to the barrel was begun, While in my improved construction the 5 buier pressure builds up principally thereafter.

In the prior construction, the point of applica tion of the initial barrel extension pressure effective in accelerating the bolt occurred at a line which was about one half the radius ofthe conl0 tact between the accelerator tip and bolt and was `discontinued at a point approximately Aq the radius of the point of first application of accelerating force. In my improved accelerator the point of application of initial accelerating pressure between the barrel extension and accelerator is much higher, and moves rapidly toward the pivot of the accelerator, but continues to a point on the accelerator having a radius on the accelerator which is less than the radius of the correspond- ,20 ing bearing in the prior gun, and is less than V3 of the radius of the first point of accelerating i pressure from the barrel extension. While this attainment of improved tra'rl'slerV ol motion is effected and completed before the bar'-vr rel extension' has been Ycompletely* stopped, it still stored or dissipated by the oil or other barrel buffer, As is the case of the prior gun coiistruce tiony the shift in the point of pressure of the barrel extension on theaccelerator is necessary in order that by the' increased ratio of movement of the accelerator tip accelerating force will com y tinue to be applied to the bolt as the latter is accelerated and the barrel extension decelerated.

The construction of my accelerator is so iinproved that on counter=re`coil, 'after unlocking of 4.0 the accelerator from the barrel extension shank,

there is less possibility of free play of the accelerator tip in the claw recess. And there is also a reduced liability of blocking of the accelerator and bolt by engagement of the claw against the under side' of the bolt at the locking' notch, as

occasionally happens lin the prior gun.`

Additional objects, advantages, and features of invention will bev apparent or understood from the following description and accompanying drawings, and also reside largely in the' construe tion arrangement and formation of the parts for co-a'ctive operation, particularly with respect Vto timing in the cycle of operations relative to the corresponding timing of the same or equivalent parts in the prior' mechanism. Objects, advantages, and features of invention will also be largely apparent from the accompanying drawe ing, wherein:

Figure 1 is an elevational view of thev g'un,

partly `in section;

Figure` 2 is a longitudinal section of the receiver enlarged, showing the parts recoiled;

Figure 3 is a similar view showing the parts in battery;

' Figure 4 is an enlarged perspective detail of the accelerator;

Figure 5 is a view showing the plotting development ofthe cam;

" Figure 6 isan enlarged partly diagrammatic and fragmentary vertical longitudinal sectional View of the coupled parts of the barrel extension and bolt i'n the improved gun; the bolt, the accelerator, and the associated engaging parts being shown at the moment of initial simultaneous the accelerator, in course of recoil, the relation ofl the bolt and barrel extension when locked being dotted (the hooks of the accelerator being omitted).

Figure 7 is a similar view showing the same parts at a slightly farther advance recoil position; 4Figure 8 is a similar view showing the parts still farther advanced, at termination of acceleration of the bolt, a yet further stage of movement being shown in dotted lines in which the accelerator pressure on the bolt is relieved, and the accelerator is being propelled by the bolt.

Figure 9 is a fragmentary longitudinal sectional view corresponding to the diagram in Figures 6, 7 and 8 at a farther advance recoil position of the bolt and with the accelerator in locked relation to the barrel extension shank and buffer spring, this being the extreme of rearward movement of the accelerator.

Figure 10 is a fragmentary cross section on the line lil- I0 of Figure 9.

Referring more particularly to the drawings, there is illustrated in Figure l, a gun embodying my invention in the general construction before referred to and disclosed in said patents. In this figure reference numerals 20, 2|, 22 and 23 designate the receiver, the barrel, a recoil booster and a bolt buffer, all of conventional construction as heretofore used in said guns and which are only generally shown, no details ythereof being included in this application, since they each serve the usual purposes of corresponding elements in prior use. The recoil booster has the general purpose of increasing the recoil force acting upon the barrel, thus adding an increment to the forces heretofore available for reaction of the cartridge against the pressure plate of the bolt, and resulting in a more rapid recoil of both the bolt and barrel extension in that part of the movement of the last named two parts in which they are locked together, and with the additional consequence that the acceleration of the bolt upon release from the barrel extension is correspondingly increased.

There is also generally shown in Figures 2 and 3, a barrel buffer 24, which is preferably an air or spring buffer, in which oil is omitted and a more resilient and effective action in the stoppage and return of the barrel extension is attained. Both forms of the device being well understood, their details are not illustrated or discussed in detail although the lconnection between the dasher and the barrel extension is illustrated at 21 and referred to hereinafter.

' The gun as specifically illustrated includes some other modification contributing to safety and avoidance of excessive wear and fracture as well as improvement of function. These, while being in part referred to, comprise no novel features of the vpresent invention, and are not described in detail or claimed herein.

Among the features of distinction from the prior gun which involve some re-arrangement and modification of form, without however, changing the general dimensions of the principal operating parts of the gun or manner of their inter-actions and functioningare the following:

A breech lock depresser cam 25, with a concave curved forwardly presented cam face, is mounted by means of a base plate 26 upon the side plate of the receiver whereas, heretofore, a somewhat similar depresser finger was mounted solely upon the body of the oil buffer'. The foregoing features, andalso others, are more specifically explained and'described in a co-pending application of An derson and Pierce, Serial No. 579,736, filed February 26, '1945. As there stated, the breech lock cam has been modified, the extractor cam of the prior gun has been somewhat modified in shape, as Well as the extractor lifter cam, the side plate switch, and the switch for the belt feed lever improved.A Various mountings for bearing parts, contributing to longer wear, greater strength, and less shock in operation have been improved and are described in said other application.

In connection with the present invention, the bolt has been lightened by removing a large amount of material, which in itself lessens shock of stoppages and acceleration, while retaining the benefit of adequate mass when associated with the greater momentum developed. The bolt weight has been reduced from 41/2 lbs., in the prior gun to approximately 3%, lbs., for the new gun.

The bolt 30 in this device has the same general form of body and dimension as the prior bolt, and functions in the same manner in the extraction of rounds from the belt, loading, firing, and ejection of cartridge cases. It also carries a generally similar ring pin assembly, with corresponding sear and cooking lever.

The bolt 30 as heretofore, has a smooth-finished planiform under face 34 extending throughout the major part of its length, continuously from the forward end under the T-slot to the locking notch 3| (which is in its usual location near the rear end of the bolt), and then beyond this notch to a claw tip receiving recess 32 extending somewhat higher into the bolt than the notch 3|, and of the same dimension as the corresponding recess heretofore. The rear side of this recess is formed by the same general form of striker lug 33 comprising, as heretofore, an integral part of the bolt. This lug extends downwardly to a distance below the level of the bottom face 34 on the bolt suicient to lie well below the center of the rounded end or tip of the retracted claw when the latter is in its rearmost position. The forward side of the lug is termed a, presser face 31 since the accelerator claw presses against it in 'accelerating the bolt.

The accelerator |00 comprises a partly cylindrical base or hub part 4i), having an axial transverse bore 4l fitted revolubly on the accelerator pin 42, which, as heretofore, is set a-cross the lower part of the buffer body 43 close to the bottom of the receiver. The buffer body 43 is held in the receiver in the present instance by being set between the rear end of the breechlock cam 44 and the back plate 45 of the receiver, by the prior rear lugs on the body set in groves in the side plates of the receiver, and by rear end portions of the new depressers 25 (fixed on the receiver) set in the longitudinal channels in the forward end of the buffer body which previously alone held the depressers. Vertical play of the forward end of the buffer body heretofore manifest is thereby eliminated.

The breechlock cam 44, as before, is co-eXtensive in width with the accelerator and -bevelled across its rear end as at 46 to clear the cam faces 41 of the accelerator as heretofore. The hub is formed with a fiat 48 at its forward side which, at the rear position of the accelerator, is aligned with, or located rearwardly of, the end of the body 43, to permit full recoil of the barrel extension 50. The hub has also a rear llat 49 which is wiped by the leaf spring 49 called the buffer tube lock, this at and spring being the same, and having the same functions as in the prior gun.

Asshown in Figures 2 and 4, the accelerator is vertically slotted in its outer part as at `5| so that it may straddle the barrel extension shank 21 Which extends past the accelerator to the piston rod 28 of the buier, to which the shank is separably connected as heretofore. This produces two identical claws 52 on the accelerator which are convex on their forward sides, producing the cams 41, and are concave as heretofore for part of their transverse thickness on the rear sides, having respective rearward hooks 53 of conventional form, location, and function, projecting beside the slot 5I to wipe the lateral ends of the T-head piece 54 of the barrel extension shank 21. On recoil, these claws are moved by the bolt downward until the hooks are in a dead center relation between the pin G2 and head 54. The accelerator is then in its rear low position, inclined upward from its pivot, the undersides of its tips resting on a bevelled top surface 56 of the buer body 24, as in Figures 2 and 9. The spring 48 then bears upward on the forward part of the flat i9 in such manner as to prevent loose play of the accelerator and slightly opposing its return from this rear low position.

It should be noted that in the last named position the thickness of the tip 5%5 of the claw is such that while resting on the buffer body 43, its uppermost tip or cam surface 41 is very close to the bottom face 3d of the bolt, barely clearing the lattel. In the prior construction, as before indicated, there ywas a clearance here between bolt and accelerator at this stage of operation, of one eighth inch more or less, permitting oscillation and hammering of the accelerator against the under side of the bolt during the nearly five inches recoil travel and return of the bolt after rearward an overall ien-sth of approximately two and a quarter inches in the improved gun described may be mainly produced with two simple curves, their junction being on common tangents of different radii. A point c is taken for the axis of the bore 4|, and the nai is estabusned by a une b spaced from the point a a distance determined by the proximity of the forward end of the buffer body to the pin 42. The line b is parallel to one dropped from the point a divergent from a vertical in the direction of the line b at an angle of 142. This is approximately the orientation of the flat 48 when the accelerator is at its rear limit resting on the buffer body, as in Figures 2 and 9 A point c is next established for the radius of the major and lower part of the lcam face 111 from near the line b upward. This point is 1.69 inches below a horizontal through. the axis point a, and 2.962 inches from a vertical through a in the direction of the concave side of the claw (toward the left in Figure 5). Using c as a center, and a radius of 3.82 inches, a curve d is then drawn upward from the line b, representing the lower part of the cam face 41.

A third center point e is then established 1.246

inches above said horizontal and .905 inch from said vertical in the same direction therefrom as the point c (to the left in Figure 5) and anarc .f of .140 inchl radius on this center drawn from a vertical through e at the upper side in the last named direction and downwardly a suitable distance to merge with the line g representing the concave surface of thev claw, which may be substantially as heretofore constructed` The lines for the contours of the hooks 53 may also be developed conventionally. The arc represents a slightly greater radius than the corresponding curve in the prior accelerator, but its center c `is slightly closer to the pivot axis a of the accelerator. The forward cam contour is completed by drawing an arc h coincident with the beginning of arc f and with a radius of .700 inch centered below at i, on a vertical through the point e. This joins curve d on common tangente. The junction between the lower cam face and ilat 48 is completed by an arc 7c (defining the heel 51), having a radius of .25 inch centered on the said vertical through point a and coincident with the line b and arc d. The curves d and k may be drawn before the line b as a means of establishing the latter, if desired. The sector m representing the cylindrical segment of the hub lll is drawn with a radius of .480 inch, from an intersection with the line 47J and may be used for locating the center for the arc g which has a radius of 1.062, centered close above the horizontal through a.

In the operation of the gun constructed and assembled as described, the firing mechanism operates substantially as heretofore, and by a simiiar trigger means, using the same ammunition. Upon iring of a round, the reaction upon the cartridge is transmitted to the bolt as heretofore. augmented by the added component incident to the functioning of the booster. The bolt and barrel extension then move rearwardly in locked relation until, when the bolt lock 35 is rearwardly of the bolt lock cam lobe M', the depresser device 25 engages the breechlock pin and lowers the lock immediately. The bolt is thereby freed from the barrel extension as to 1ongitudinal movement, although without immediate movement relatively thereon. A slight retardance of the barrel extension by the buffer 24 causes a relative slowing of the barrel and barrel extension and consequent slight relative movement of the bolt rearwardly on the barrel extension. Earlier, before unlocking, the vertical rear bearing face 3E of the barrel extension will have engaged and raised the tip of the accelerator, so that it enters the claw recess 32 and quickly assumes a position at which it bears at 60 on the bearing face 36 of the barrel extension, and simultaneously at 6| on the presser face 31 of the .lug 33 of the bolt. The relative rearward movement of the bolt on the barrel extensionat this moment is so slight (perhaps .04 inch) that simultaneous or coincident bearing at faces filand 31 may be said to occur during coincidence of motion of the bolt and barrel extension. Acceleration of the bolt is thus begun, but the initial `effective bearing of face 36 on the cam face 4l' is at a high front line 60 so very near the level of the rear high line 6| of bearing between the claw tip 55 and the presser face 31, that there is very close approximation of coincidence of motion of the engaged parts of the accelerator with the bolt and barrel extension at the same time.y This results in avoidance of shock in the beginning of acceleration of the bolt, as may be appreciated. The continuance of rearward movement of the barrel extension and bolt, carrying the accelerator toward a rearward inclined position, now rapidly lowers the line of contact between the bearing face 36 of the barrel extension and the forward cam face 4.1 of the accelerator from the initial high line 60, but'there is much less lowering of the contact between the tip 55 of the accelerator and the presser face 31, so that a great increase of leverage occurs, and a of the tip 55, notwithstanding progressive deceleration of the barrel extension by the buffer 24 (the decelerating effect of the conventional drive spring 62 on the bolt is immaterial at this time). Thus, a sustained application of force to the bolt is maintained, and its acceleration likewise continued in the manner illustrated in Figures 6, 7, and 8. In the last mentioned View the line contact between barrel extension and the cam face 4T of the accelerator has been lowered to the heel portion 51 marking the rounded juncture between tlie cam face lll proper and the flat 48. Thereafter, this heel line of contact, moving upwardly on an arc, decreases the mechanical advantage, so that no further acceleration is applied to the bolt and the bolt -continues its movement by momentum while the final movement of the barrel extension becomes progressively less over .07 9 inch, more or less, of distance to full stopped position of the barrel. Continuance of movement of the bolt now causes the forward lower corner B of the claw recess 32 (which has earlier engaged the forward side of the claw tip) to continue movement of the accelerator to its rear lowered position as in Figures 2 and 9, The bolt passes closely over the cam 41, and continues its recoil movement for a distance of approximately 4 inches farther until it is stopped by the bolt buffer 23, and its counterrecoil begun. In the counterrecoil of the bolt, its presser face 3T finally reaches the tip of the accelerator, pressing the same forwardly, and lifting it so as to free the hook 53 from the shank head 54 and permit reaction of the buffer spring. The latter then begins ccunterrecoil of the barrel extension and barrel. At about the same time, the accelerator will have been moved by the bolt to a position where the heel of the cam again engages the bearing face 36 of the barrel extension, and aids in acceleration of the barrel parts, the mechanical advantage of this leverage gradually 'increasing in a ratio the reverse of that by which it decreased on recoil of the bolt. Thus, the barrel extension is quickly brought into coincidence of forward motion with the bolt at about the time when the lock notch 3! of the bolt is aligned with the breech lock 35 in the barrel extension, and the lock engages the lifting lobe of the breech lock cam M. relooking the bolt and barrel extension. From that time, the counterrecoil proceeds substantially as in the prior weapon, except that it occurs at a greater rate of speed, until the bolt rea-ches battery position. There, in automatic fire, a newly chambered round is lred, the ring of the primer having occurred slightly before the parts reached battery position in accordance with prior practice.

As the forward side of the recess 32 presses the accelerator rearwardly to its rear low or retracted position, the hook A53 wipes upon the head ofthe barrel extension shank, camming the same rearwardly and the hook reaching or passing dead center relation thereto and being additionally retained by the buier tube lock spring 49.

It should be noted that by the particular plotting of the forward cam face of the accelerator as described, the break from the longer radius portion d to the part h of shorter radius near the tip produces a material thickening and raising or bulge of the surface 41 of the cam as compared to the prior cam, resulting in effecting the high linev contact 6l) thereby (indi-cated by solid arrow in Fig. 6) at a level on the barrel extension much higher than that of theA corresponding early or high level contact of the prior accelerator (indicated by dotted arrow),y and involving also a higher level of the top face of the tip of the retracted accelerator lll under the recoiling and counterrecoiling bolt. The curve for the cam face may be plotted by other methods if desired, and may vary somewhat from the exact form described without material detriment, but should conform to the limitations as to very high and very low lines of contact between the barrel. extension and accelerator and the relation of these to the bearing atthe rear side of the tip of the accelerator. 1

With the improved accelerator, as acceleration progresses, the bearing between the face 35 of the barrel extension and the cam 4l continues over a longer distance in the travel of the bolt, and to a lower level (indicated by solid arrow, Fig. 8) than were `attained in the bearing of the barrel extension on the prior accelerator, the latter extreme being indicated by dotted arrow in Fi'g. 8; The difference in the lines of bearing of the barrel extension on my accelerator and on the prior one at an intermediate stage between the above extremes is indicated, respectively, by the solid and dotted arrows in Fig. 7.

It appears from operation of the gun as constructed with the improved accelerator that the line 60 is at a radial distance from the axis of the accelerator which is at least three quarters of the corresponding distance between the rear high line 6I and said axis, measured at the instant when the simultaneous or coincident bearing of the barrel extension and bolt on the accelerator is initiated in recoil of the parts.r

The first measurement (at 60) is at least more th'an two thirds the length of the second measurement (at 6l). Also, the radius of the high line 60 is approximately ve times the length of travel of the barrel extension during acceleration ofthe bolt, or R=5a, where R is the radius of said high line on the accelerator, and a the distance travelled by the barrel extension during acceleration of the bolt; and the radius of the heel 5'! is approximately twice the distance of said travel of the barrel extension.

The foregoing is intended to disclose in full detail a construction of mine embodying' the invention upon which this application is predicated, this construction having been hereotfore produced and used inquantity in the national defense, but it will be understood. nevertheless that this is largely exemplary andthat modications of the structure, arrangement and proportions of the parts. substitution of materials and-equivalentsmechanical or otherwise, may be made. and expedients of making separate vor integral carried out without departing from the spirit of the invention hereinafter claimed.

I claim:

1. In a gun of the character described wherein there is a receiver having a'reciprocating recoiling barrel and a farther reciprocating breech bolt, means to lock the bolt and barrel in fixed relation at battery and over a part of their movement from and to battery, wherein the bolt and barrel are unlocked at a predetermined part of their recoil a distance rearward of battery; an extension on said barrel, a lever-like accelerator pivoted below the bolt on a fixed axis in the receiver for movement between said barrel extension and bolt, said barrel extension having a rearwardly tension through the accelerator when the latter is in a predetermined part of its movement, the accelerator having a lowered rear positionv at the rear limit of its movementv in the path of and yieldable'upwardly to said presser face ofthe bolt in counterrecoil, said accelerator having an ex treme forward upwardly inclined position against said bearing face with its tip below the'bolt whereby rearward movement of said barrel part will cause the accelerator to slide upward on said bearing face to a high front line on the accelerator and to simultaneous effective bearing relation to said presser face after not more than approximately .04 inch of 'relative movement of the bolt from locked relation tothe barrel part, said accelerator including a claw portion having a tip with a rear face opposed to said presser face to engage the same at a high rear line at the instant of said simultaneous eective accelerating engagement of the bearing face at said high front line, said claw having a convex cam face shaped to receive said bearing face there against at said high front line, said accelerator characterized in having a horizontal fore and aft dimension between said lines at said instant, equal to the' corresponding horizontal :distance between the said bearing face and presser face Aat said instant, but greater by .04 inch `rnore or less, than the distance between said bearing and presser faces when the bolt and barrel are in mutual locked relation, the tip of said claw being tapered suicient for free entry between the said bearing :and presser faces at said locked relation of the parts, the forward face of the accelerator being progressively decreased in radius from said highv front lin-e thereon to a low elective bearing yline thereon of minimum radius, the radius 'of the said high front line being more than three quartersthe radius of said high rear line on the accelerator and approxiA mating R=a where R is the radius of said high front line and a is the total distance of movement of the barrel extension in accelerating relation to the bolt, the radius-oi said low line being less than one third or the -rst mentioned radius.

2. The structure of claim 1, wherein said presser face is extended below said lowered rear position of the accelerator tip, saidbolt having a horizontal bot-tom vface extending forwardly from adjacent the presser `face, sai-d accelerator being fur-ther characterized by a cam face bulging upward at said position so as to lie closely under said bottom face to prevent oscillating action of the accelerator duri-ng recoil after acoelenation and duri-ng comiterrecoil betere raising of the accelerator.

3. The structure of claim l, wherein said vpresser face is Vextended below the 'level of the accelerator tip when at said lowered rear position, said bolt having a horizontal bottom face :extending forwardly .from .adacent the presser face at -a level to l-ie closely `and slirlably over the accelerator when at said lowered rear position to prevent oscillating action of the accelerator during recoil after acceleration and during counterrecol before raising of the accelerator, said bottom face being recessed before the presser face to receive thetip of the accelerator a distance above said bottom face, the forward side of said recess constituting a shoulder spaced from said presser -face at such level and of such shape as to conform to fore and aft measurements of the accelerator at the same level throughout a limited rear part of movement of the accelerator tip while in said recess whereby to limit loose movement of the accelerator in said recess. f

4. In a rapid. iire machine gun; a receiver, a reciprocating barrel therein, a reciprocating breech bolt independently reciprocaole therein, a barrel buffer and counterrecoil spring means for the barrel, a buffer and drivin spring means for the bolt, positioned to be clective later in the recoil cycle than the barrel buffer, an accelerator pivotally supported in the receiver to swing against the bolt through part of the movement of the latter for accelerating the recoil of said bolt, a barrel yextension having a bearing surface substantially transverse to the line ci recoil and moveable in recoil to actuate said accelerator by bearing thereon during the pivotal movement lthereof agm'nst the bolt, said accelerator having a leading earn edge for engagement with said barrel lextension bearing surface, the contour of said leading cam edge being such as to initially ulcrum on said bearing surfaces at a radial clistan'ce from the pivotal axis of said accelerator which bears substantially the same ratio to the corresponding distance to the line of bearing between the accelerator aXis of the bolt when the accelerator initially engages the bolt acceleratively as the ratio of barrel speed to bolt speed at this inst-ant, said contour being shaped to progressively :reduce said radial fulcruni distance said 4barrel extension continues its recoil motion, whereby the bolt progressively and smoothly .accelerated relative to the barrel as recoil proceeds.

5. The invention .as recited in claim 4, including breech bolt means for locking said bolt and barrel extension together, breech lock operating means mounted in the receiver tc loclz said loci: on approach to battery over a terminal part of such movement and to unlock at a corresponding part of .the .early recoil movement to insure engagement .of the accelerator by the barrel extension.

' CHARLES E. BALLEISEN.

REFERENCES CITED The lfollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,293,021 Browning Feb. 4, 1919 2,110,165 -Moore Mar. 8, 1938 2,337,273 Robinson Dec. 21, 1943 

